Author Topic: SDA /SDT Generator Manual copy available and question on de-magnetised generator  (Read 14778 times)

listeroil

  • Full Member
  • ***
  • Posts: 208
    • View Profile
Alex
Sorry to butt in at this late stage but I have read through all the pages of this post and think you need to take a fresh look at your problem.  I have been running these for 18 years and have rebuilt a few and this is a simple way of checking if your windings are ok.

When you start a generator with one of these dual function alternators you feed 24 volts into start windings which also feeds the main field winding as well which is the same as flashing the winding.  So no need to flash the aux winding for any reason on these units.
 
What I would suggest is that you connect a 100 watt 240v incandescent light bulb directly to the 2 AC brush connections in the generator.  Then start the engine and see what happens. The bulb should light up and stay lit when starter is released.

When I rebuild mine I do this before connecting the generator to the engine and use the starter function to spin the generator up.  What happens is that as the revs increase the light get brighter and brighter as the revs build up.  When I disconnect the start connection the bulb looses a bit of brightness but stays lit until the generator run down.  If yours does this the windings are okay and your problem lies elsewhere.
Mick

ajaffa1

  • Hero Member
  • *****
  • Posts: 1402
    • View Profile
Hi Mick, please don`t feel that you are butting in, any and all good advice that we can give to Alex will be appreciated.

Alex I will have a good look through your findings and get back to you this evening. From a very quick look I believe we have a pair of wires mixed up on the bridge rectifier. The good news is that you have continuity between the slip rings, so those windings are OK.

Bob

Alexdick

  • Jr. Member
  • **
  • Posts: 60
    • View Profile
great, many thanks! I look forward to hearing from you.
Mick, I will give that a go to but would be grateful if you could let me know which the two AC brush connectors are! Thanks
Alex

listeroil

  • Full Member
  • ***
  • Posts: 208
    • View Profile
Alex

The AC brush connections are the ones that go to the slip rings.

Mick

mikenash

  • Hero Member
  • *****
  • Posts: 849
    • View Profile
People like me who have a few gen heads but know nothing of their innards could learn a lot from this thread and it's digressions

I wonder if it is WOK material?

It seems to me there's good basic stuff here I might like to refer to later - so possibly others are in the same boat?

Cheers

ajaffa1

  • Hero Member
  • *****
  • Posts: 1402
    • View Profile
Hi Mike, if I ever get the time it might be worth doing a complete strip down and rebuild of my Brush generator head. I could then post photos, wiring diagrams and resistance figures. There seam to be quite a lot of these generators still in out there.

Hi Alex, I was a little baffled by some of the readings you sent me. Having studied the wiring in your top box, the neutral and positive AC outputs on yours are different to mine, reversed. Thus 1 and 13 are reversed on your model. Please check the resistance between 13 and 2, also the resistance between 1 and 12 and get back to me.

The other thing that concerns me is that you do not have continuity between the slip ring (11) and the brush holder (12), could you please check the condition of the brushes, holders and wiring connections then check the resistance again.

Bob

dax021

  • Full Member
  • ***
  • Posts: 176
    • View Profile
Bob, that would be great, please find the time.  From reading this thread, it would seem that the Brush unit is pretty much the same thing as my Hoffberg, and i would really like to know more and upgrade/modernise the thing.

ajaffa1

  • Hero Member
  • *****
  • Posts: 1402
    • View Profile
Hi Dax021. I`m happy to do the disassembly and rebuild and document it for others. I just can`t do it any time soon due to the threat of rolling blackouts. Between the government, big business and environmental groups they have contrived to produce an electricity shortage in a country with the highest coal reserves on earth. High prices, low reliability and no investment for the future. The generating companies are coining it in, the government are doing the same. Small businesses are going belly up and house holders are footing the bill and sweltering in houses without power, large energy consumers like steel and aluminium smelters are being asked to shut down production.

I`m expecting to need my generator in serviceable condition for the immediate future. Happy to do the documentation once silly season has passed.

Bob

Alexdick

  • Jr. Member
  • **
  • Posts: 60
    • View Profile
Bob

I look forward to this....I feel it wouold be best to strrip mine down as there is so much cr#p in it (dust etc) and some of the wires have been chewed. Perhaps I should do this anyway so we can get some decent resistance readings using the new wires, screws etc?! I might as well paint it at the same time! Mechanically it is fine and was generating electricity perfectly until i let it run down with the load still attached. I am not worried about powercuts so don't have to wait to do the job (and its not generating anyway as you know!)
Alex

ajaffa1

  • Hero Member
  • *****
  • Posts: 1402
    • View Profile
Hi Alex, I feel like I have let you down somehow, we should have this sorted out by now but it is difficult to diagnose problems from the other side of the world. We will get there in the end. I am glad that the UK power supply is stable for the time being. The UK is currently importing large amounts of electricity from the continent and has ramped up it`s coal fired generation to deal with demand during the cold weather.

Nuclear power stations and coal fire plants are at the end of their useful lives so there is going to be a shortage, lack of government forward thinking has caused two nuclear projects to be canned. Just imagine how popular you will be when you are the only house in the street with power.  :laugh:

Bob

Alexdick

  • Jr. Member
  • **
  • Posts: 60
    • View Profile
Bob

Please do not feel that you have let me down.....quite the opposite!
I will get back ASAP with the resistance readings and we can take it from there.
thanks again
Alex

Alexdick

  • Jr. Member
  • **
  • Posts: 60
    • View Profile
Hi Mike, if I ever get the time it might be worth doing a complete strip down and rebuild of my Brush generator head. I could then post photos, wiring diagrams and resistance figures. There seam to be quite a lot of these generators still in out there.

Hi Alex, I was a little baffled by some of the readings you sent me. Having studied the wiring in your top box, the neutral and positive AC outputs on yours are different to mine, reversed. Thus 1 and 13 are reversed on your model. Please check the resistance between 13 and 2, also the resistance between 1 and 12 and get back to me.

The other thing that concerns me is that you do not have continuity between the slip ring (11) and the brush holder (12), could you please check the condition of the brushes, holders and wiring connections then check the resistance again.

Bob

Bob

 I have the readings.....between 13 and 2 is 1.9 ohms and between 1 and 12 is 0.5 ohms......
As the neutral and positive AC outputs are opposite to yours, could i have put everything back together back to front when i replaced the bridge rectifier etc?
I have checked between 11and 12 again...it shoots up to a reading between 107 and 170 ohms and then drop back to 1 ....
i am confused!
alex

ajaffa1

  • Hero Member
  • *****
  • Posts: 1402
    • View Profile
Hi Alex thank you for your findings. I am a little confused by the resistance reading between 11 &12 (slip ring and slip ring brush holder), I suspect the brushes and slip rings may be a little dirty causing the anomalous reading.

I would like you to check the connections on the new rectifier.

What I would like for you to do is undo all the lugs on the new bridge rectifier. Remove the four large wires, you can leave the two small black wires that connect to the rheostat. Using your multi-meter, on Ohms, put the black probe on 13 and then touch the red probe on all of the four loose wires, one by one. One of them should read 0.1 ohms. Connect this wire to number 2 on your new rectifier, along with the wire to the rheostat. Please check that this terminal has the sine wave symbol next to it.

This leaves you with three wires please use your meter to test between these wires, two of them will make a circuit with a resistance of 0.3 to 0.4 ohms. These two are the auxiliary field windings, the longer of these two wires should be the +ve and needs to be connected to number 7 (please check it has a + sign). The shorter of these two wires is the -ve  and needs to  be connected to number 8 (please check it has a -sign).

This will leave you with only one wire this needs to be connected to number 6, along with the small wire to the rheostat.

Now please check the resistance between 1 and 13 you should have a circuit showing around 4 ohms.

Bob


Alexdick

  • Jr. Member
  • **
  • Posts: 60
    • View Profile
Hi Bob and apologies for the delay in replying.
Ok, I have done everything you asked and the readings were slightly higher than yours. However, on the final task (measuring between 1 to 13) things go wrong. the meter jumps to about 26 ohms instantaneously and then drops back to 1 .....i feel the whole generator probably needs rewiring!?
thanks
alex

ajaffa1

  • Hero Member
  • *****
  • Posts: 1402
    • View Profile
Hi Alex, nothing to panic about. The important thing is that you now have continuity between 1 and 13, so it should be able to generate electricity. The slightly odd reading you get might be caused by dirty brushes or slip rings, it could also be caused by the two radio frequency condensers if they are still connected or it might be that the very low voltages produced by a multi meter are not high enough to quickly trigger the diodes in a bridge rectifier rated at 400 volts 60 amps.

Could you please check the resistance between 13 and 14 (black probe on 13) should read 0.1 ohms, 13 and 15 (black probe on 13) should read 2.7  ohms, 13 and 16 (black probe on 13) should read 0.3 ohms and lastly 13 and 17 (black probe on 13) should read 0.1 ohms.

Let me know what you get, no surrender!

Bob